1. Field of the Invention
The present invention relates to a secondary battery with a protective circuit module.
2. Description of the Prior Art
Generally, as portable wireless devices such as video cameras, cellular phones, portable computers, and the like have become more lightweight and increasingly developed, research has been conducted on secondary batteries used for driving such devices. Secondary batteries are rechargeable and can be compact, yet have a high capacity. Conventional secondary batteries may be, for example, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries, and the like. Lithium secondary batteries are widely used among other reasons, due to their high operating voltage and high energy density per weight.
Secondary batteries may be classified into cylinder type batteries using a cylindrical aluminum can, rectangular type batteries using a rectangular aluminum can, and pouch type batteries housed in a thin pouch case.
In rectangular secondary batteries, a bare cell is formed by stacking an anode plate, a cathode plate and a separator and winding them to form an electrode assembly. The electrode assembly is then inserted into a rectangular metal can, and an open portion of the rectangular can is sealed by a cap plate to form a bare cell. Furthermore, an insulated electrode terminal is provided on the cap plate, wherein the electrode terminal forms one electrode of the secondary battery, and the cap plate and the can form the other electrode.
A protective circuit module (PCM) including a secondary protective element such as a positive temperature coefficient (PTC) element and a protective circuit board may be mounted on the upper part of the bare cell as a safety device for the secondary battery.
The PTC element functions as a conductor at normal temperature, and but ceases to function as a conductor when electric resistance is increased in proportion to increased surrounding temperature or is otherwise subjected to relatively high temperatures. Typically, the PTC element is connected to the protective circuit board by spot welding.
In conventional secondary batteries, after an electrically conductive nickel (Ni) plate is attached to a protective circuit board, a PTC element is coupled to the electrically conductive plate by spot welding. In order to couple the PTC element to the protective circuit board, equipment, such as a welding jig, is needed, and a relatively complicated connection operation is required. Further, since the electrically conductive nickel plate is attached to the protective circuit board by surface mount technology (SMT), the production cost of the secondary battery is relatively high. Additionally, due to the relatively high temperature applied to the PTC element by welding during assembly, the functionality of the PTC element may deteriorate.